Asymmetry compensation apparatus and reproduction apparatus for recordable disc

Abstract

When a linking-point indicating signal, a defect detection signal, and a peak detection signal are obtained, a switch control section controls the on/off states of switches such that the time constant of a filter section becomes smaller or larger than the standard value during the specified period. With this control, in a linking section or a period in which a reproduced signal is missing, the threshold for asymmetry compensation traces a signal state at a higher speed, or the preceding threshold is maintained irrespective of the state of an input signal.

What is claimed is:  
     
       1. An asymmetry compensation apparatus comprising: 
       input level detecting means for making a detection signal obtained by comparing the level of a reproduced signal read from a disc-shaped recording medium with a threshold to a binary signal and for outputting the binary signal as a reproduced data signal;  
       asymmetry compensation means provided with a low-pass filter to which the detection signal is input from said input level detecting means, for compensating for asymmetry generated in the reproduced data signal by inputting as the threshold the output of the low-pass filter to said input level detecting means;  
       signal state detecting means for detecting a state in which the state of the reproduced signal matches the specified condition; and  
       time constant changing means for controlling such that the time constant of the low-pass filter is changed at the specified timing when said signal state detecting means detects a state in which the state of the reproduced signal matches the specified condition.  
     
     
       2. An asymmetry compensation apparatus according to claim  1 , wherein said time constant changing means changes the time constant of the low-pass filter according to a change in the state of the reproduced signal detected by said signal state detecting means such that the threshold changes so as to allow higher speed tracking than in the standard case. 
     
     
       3. An asymmetry compensation apparatus according to claim  1 , wherein said time constant changing means changes the time constant of the low-pass filter according to a change in the state of the reproduced signal detected by said signal state detecting means such that the preceding threshold is substantially maintained during the specified period. 
     
     
       4. An asymmetry compensation apparatus according to claim  1 , wherein said signal state detecting means detects a state in which a reproduced signal input to said asymmetry compensation apparatus corresponds to link areas inserted in units of the specified data. 
     
     
       5. An asymmetry compensation apparatus according to claim  4 , 
       wherein said asymmetry compensation apparatus handles a disc-shaped recording medium in which a data-recording track is wobbled according to a frequency modulation signal having address information;  
       said signal state detecting means includes:  
       position information storage means for storing the recording position information of the link areas on the disc-shaped recording medium; and  
       address information extracting means for extracting address information from a reproduced signal obtained by reproducing the wobbling of the track; and  
       a state in which a reproduced signal input to said asymmetry compensation apparatus corresponds to the link areas is detected by comparing the recording position information with the address information.  
     
     
       6. An asymmetry compensation apparatus according to claim  4 , 
       wherein said signal state detecting means includes data contents identifying means for identifying the specified data contents in a reproduced data signal and  
       said signal state detecting means predicts the timing at which a reproduced signal input to said asymmetry compensation apparatus corresponds to a link area, according to the data contents.  
     
     
       7. An asymmetry compensation apparatus according to claim  1 , wherein said signal state detecting means detects a state in which a reproduced signal input to said asymmetry compensation apparatus is missing. 
     
     
       8. A reproduction apparatus for reproducing data by making a reproduced RF signal read from a disc-shaped recording medium to a binary signal and for applying the specified demodulation processing to the binary signal, comprising: 
       a waveform processing circuit for producing a binary signal by comparing the reproduced RF signal with a threshold; and  
       a demodulation circuit for demodulating the binary RF signal,  
       said waveform processing circuit including: comparing means for comparing the reproduced RF signal with the threshold; and filter means for receiving the output signal of the comparing means and for changing a time constant according to the reproduction position on the disc-shaped recording medium where the reproduced RF signal is detected.  
     
     
       9. A reproduction apparatus according to claim  8  for the disc-shaped recording medium having a track which is wobbled according to address information and in which link areas are inserted in units of the specified data, further comprising: 
       address information extracting means for extracting the address information from a reproduced signal obtained from the wobbling of the track;  
       storage means for storing the position information indicating the recording position of the link areas; and  
       control means for changing the time constant by comparing the address information with the position information.  
     
     
       10. A reproduction apparatus according to claim  9 , wherein said control means changes the time constant of said filter means such that the threshold changes at a higher speed than in a case in which a signal is sent from an area other than the link areas, when said control means detects a state in which the reproduced RF signal is sent from an area other than the link areas. 
     
     
       11. A reproduction apparatus according to claim  8  for the disc-shaped recording medium having a track including link areas inserted in units of the specified data and a plurality of sectors to which frame synchronization signals are inserted in units of data frames, further comprising: 
       address information extracting means for detecting the recording positions of the link areas according to the frame synchronization signals; and  
       control means for changing the time constant according to the timings when the recording positions are detected.  
     
     
       12. A reproduction apparatus according to claim  11 , wherein said control means changes the time constant of said filter means according to the timings when the recording positions are detected such that the preceding threshold is substantially maintained during the specified period. 
     
     
       13. A reproduction apparatus according to claim  8 , further comprising: 
       defect detecting means for detecting a state in which the reproduced RF signal is missing; and  
       control means for changing the time constant of said filter means according to the missing of the reproduced RF signal.